From: | John A Meinel <john(at)arbash-meinel(dot)com> |
---|---|
To: | emil(at)baymountain(dot)com |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Planner constants for RAM resident databases |
Date: | 2005-07-02 02:40:49 |
Message-ID: | 42C5FEB1.6090601@arbash-meinel.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-performance |
Emil Briggs wrote:
>I'm working with an application where the database is entirely resident in RAM
>(the server is a quad opteron with 16GBytes of memory). It's a web
>application and handles a high volume of queries. The planner seems to be
>generating poor plans for some of our queries which I can fix by raising
>cpu_tuple_cost. I have seen some other comments in the archives saying that
>this is a bad idea but is that necessarily the case when the database is
>entirely resident in RAM?
>
>Emil
>
>
>
Generally, the key knob to twiddle when everything fits in RAM is
random_page_cost. If you truly have everything in RAM you could set it
almost to 1. 1 means that it costs exactly the same to go randomly
through the data then it does to go sequential. I would guess that even
in RAM it is faster to go sequential (since you still have to page and
deal with L1/L2/L3 cache, etc). But the default random_page_cost of 4 is
probably too high for you.
John
=:->
From | Date | Subject | |
---|---|---|---|
Next Message | John A Meinel | 2005-07-02 03:14:50 | Re: Planner constants for RAM resident databases |
Previous Message | Steve Atkins | 2005-07-02 02:08:23 | Re: Planner constants for RAM resident databases |